The present invention relates to an optical-disk recording and/or playback apparatus, an optical-disk recording and/or playback method for recording and/or playing back data into and from an optical disc-shaped recording medium and relates to a tracking control method adopted in the optical disk recording and/or playback apparatus for tracing a circular track created on the optical disc-shaped recording medium.
In recent years, rewritable disc-shaped media has become very popular. An example of such media is a magneto optical disc such as an MD (Mini Disc, a trademark).
As is generally known, on such a rewritable disc, no tracks are formed as pits. Instead, grooves and lands are created so that a track can be traced correctly by a laser beam radiated by an optical pickup in recording and playback operations.
In a groove system adopted in a conventional MD system for recording data into grooves, for example, tracks each serving as a groove are created in advance by providing wobbling based on a modulated signal obtained as a result of frequency modulation of a signal by addresses to each of the tracks. To put it in detail, surfaces on both sides of a groove are each physically formed into a shape wobbled along the circumferential direction of the disc. A groove created in this way is referred to as a wobbled groove.
In a recording/playback apparatus, tracking-servo control is executed so that a laser beam is correctly radiated to a track created as a groove or a land described above. In addition, an objective lens to which the laser beam is output is used as a means for executing focus-servo control so as to focus the laser beam on the track created on a signal surface. In the recording/playback apparatus, a modulation component representing a wobbled groove is extracted from information conveyed by a laser beam reflected by the disc to produce an address. As described above, in the recording/playback apparatus, pieces of servo controls are executed and information on addresses is acquired to implement a recording or playback operation by making accesses to the addresses.
In addition, the present applicant has earlier proposed a disc having a format described below and based on an MD format in order to implement an even higher recording density.
The format adopts a land recording system f or recording data into a land used as a recording track.
On such a disc, 2 recording tracks each implemented by a land are used as a pair and the pair of recording tracks is created to form a spiral. That is to say, on the disc, 2 lands are created to form a spiral. A wobbling shape created by modulation based on address information is thus created on each side surface of a groove formed between the 2 lands.
If this physically created state is seen from a land, a wobbling shape is created on a side surface on only one side of each of the 2 lands. That is, the pair of recording tracks implemented by 2 lands share the wobbling shape of a groove created between the 2 lands or share the address information.
Thus, in a recording or playback operation, by extracting a modulation component of the wobbling shape created on a side surface on only one side of each of the 2 lands from information conveyed by a reflected laser beam, an address can be decoded without regard to which of the 2 lands is being traced.
In a spiral track structure comprising 2 lands forming a pair as described above, the address represented by the wobbling shape of a groove formed between the 2 lands is shared by the lands. Thus, with the format for implementing a high recording density, the track pitch can be made smaller than that of the conventional MD. As a result, with this format, the recording density can be increased by for example adopting an appropriate modulation system of recorded data.
It should be noted that the address system adopted for such a disc structure is referred to as an interlace addressing system and a disc having a format conforming to this system is known as an interlace addressing disc.
By the way, in an interlace addressing disc described above, 2 recording tracks each used typically for recording data form a pair.
For this reason, it is necessary to actually carry out a recording/playback operation while forming a judgment as to which one of the 2 tracks of the pair is being traced.
The judgment as to which one of the 2 tracks of the pair is being traced will be described later in detail in the explanation of an embodiment. The judgment is formed by using a simplest configuration applying the so-called 3-beam method. The 3-beam method is one of techniques for generating a tracking-error signal used in the tracking-servo control.
By the way, an optical pickup corresponding to the 3-beam method has a problem of a large-size configuration of an optical system itself which is used for radiating a laser beam, a problem of complexity of a photo detector for receiving and detecting a reflected laser beam and a problem of complexity of a processing circuit system for processing a reflected-beam information signal output by the photo detector.
In the case of the so-called push-pull system for implementing generation of a tracking-error signal by using a beam, on the other hand, the configuration of an optical pickup including the photo detector and the configuration of the signal processing circuit system for processing a reflected-beam information signal output by the photo detector can be made simpler.
That is to say, considering the background described above, even in the case of a disc drive apparatus assuming operations to record and play back data into and from an interlace addressing disc, it is desirable to adopt the configuration of an optical pickup based on the push-pull system. If the push-pull system is adopted, however, it is impossible to form a judgment on a track by applying the 3-beam method described above. Thus, in order to adopt the push-pull system, another technique is required for allowing a target track to be traced correctly.
It is thus an object of a recording and/or playback apparatus provided by the present invention to solve the problems described above.
In order to achieve the object described above, the present invention provides an optical-disc recording and/or playback apparatus capable of carrying out operations to record and play back data into and from an optical disc, the disc comprising: first tracks including a wobbled track and a non-wobbled track each implemented by either a land or a groove where a wobbled track is a track with both side surfaces thereof wobbled whereas a non-wobbled track is a track with neither of side surfaces thereof wobbled; and second tracks each sandwiched by the first tracks and used for recording information wherein if the first track is implemented by a groove, the second track is implemented by a land and if the first track is implemented by a land, the second track is implemented by a groove, the optical-disc recording and/or playback apparatus comprising: radiation means for radiating a beam to any particular one of the tracks on the optical disc; reflected-beam detection means for detecting a beam reflected by the particular track on the optical disc; and control means for controlling the radiation means so as to have the radiation means trace a wobbled track adjacent to the particular track in accordance with the reflected beam.